http://www.magnumforceracing.com/fla...y_switches.asp
As a last resort you can always put in a battery cutoff. You can find cheaper units in Hemmings, but these are heavy duty and install in the cockpit instead of opening the hood every time to turn the battery on and off. I had an RV with the battery running down problem and the dealer never figured it out, but installed one of these. The only problem you have is the engine computer relearning every time you reconnect - this is a last resort only, but I've been there and know what you're going through.